This invention relates to a transmitting and receiving circuitry system for an ultrasonic flowmeter, with an ultrasound transducer interface for connection to an ultrasound transducer of the ultrasonic flowmeter, an amplifier with a first input and a second input, as well as a signal generator for activating the ultrasound transducer, with the first input of the amplifier connecting to the signal generator while the second input of the amplifier is connected to both the ultrasound transducer interface and, via a feedback element, to the output of the amplifier. The invention further relates to an ultrasonic flowmeter employing such transmitting and receiving circuitry and to a method for operating such transmitting and receiving circuitry.
In the operation of ultrasonic flowmeters, ultrasound waves are used for measuring the speed and flow rate of a fluid medium traveling through a measuring tube. The parameters that can be derived from the flow of the medium include, for instance, runtime differences, frequency changes and phase shifts. To that effect, ultrasound transducers transmit ultrasonic waves, in continuous or pulsed fashion, into the flowing medium and receive the reflected signals. The principles on which ultrasonic flow measurements are based essentially consist, for one, of the so-called pulling effect whereby the propagation speed of the ultrasonic waves changes as these waves are carried along by the flowing medium, and, for another, of the Doppler effect that changes the frequency as the transmitter and the receiver move relative to each other.
An ultrasonic flowmeter is usually equipped with two ultrasound transducers which are offset relative to each other in the flow direction and which can alternate between a transmitting and a receiving mode, allowing the ultrasonic waves that were transmitted by one ultrasound transducer and have traveled through the flowing medium over a certain distance to be received by the other ultrasound transducers.
As will be evident from what has been said above, a transmitting and receiving circuitry system for an ultrasonic flowmeter, meaning circuitry that must be capable of handling the transmitting as well as receiving operation of the ultrasonic flowmeter, must meet certain requirements. In particular, transmitting and receiving circuitry of that type must ensure appropriate performance, stability and an acceptable signal-to-noise ratio in both the transmitting and receiving modes. The problem lies in the fact that, to some extent, transmission and reception involve altogether different requirements for the circuitry system insofar as, in the transmission mode, the signal generator generates a voltage signal that is fed to an ultrasound transducer, enabling the latter to send ultrasonic waves into the flowing medium, whereas in the receiving mode no ultrasonic signal is generated and emitted, yet the best possible reception of an ultrasonic signal must be assured.
Conventional transmitting and receiving circuitry systems for ultrasonic flowmeters do not adequately address this problem. In particular, they fail to attain a satisfactory signal-to-noise ratio.